Built in 24 Hours: An Energy Harvesting Shoe
With a group of people I had just met at MIT's 2026 hardware hackathon, I wanted to explore an interesting concept: how can we design a prosthetic that powers itself?
With this shoe, we convert the kinetic energy from each of your footsteps to electrical energy used to power a cable-powered wearable arm assist device.
The Foot, The Belly, & The Arm
Every time you take a step, you push a compress a really stiff spring. This is our core power supply.
When you compress the spring, you are actually actuating a rack, which spins a series of gears that winds a generator (i.e. a motor).
We send the power generated from spinning the motor to charge up a lithium ion battery. When you press a button, we use this charged battery spin a motor that winds a cable to help you lift heavy objects.
Final Remarks
In truth, the amount of energy you harvest per foot-step is super small. It is something on the order of 0.01W, when you need a few watts to spin our motor. This is partly because our generator isn't great - we just grabbed a DC motor and spun it a bunch - but also because generally, converting kinetic energy to electrical energy is inefficient. It would be better to store this kinetic energy as potential energy, which you can trigger as required. We were considering this approach, but lacked a key component required by the designs we conceived: a one-way bearing. So, we jumped into an approach that seemed more doable considering our immense resource and time constraints.
In any case, I had a great time building this with my team, which consisted of an electrical and mechanical engineer from Olin, and a designer from Rhode Island. I hopped into this hackathon without knowing anybody, and I'm lucky to have found a group of people who were super motivated and friendly.